A typical rotating electric machine such as a generator includes a hollow cylindrical stator constructed by winding armature coils around a stator core and a rotor having a diameter slightly smaller than the diameter of the hollow cylindrical portion of the stator and constructed by winding field coils in a layered fashion around the cylindrical rotor core. The rotor is positioned within the stator in a co-axial manner with the stator.
The stator and rotor each has a core. An armature coil and a field coil, which are each a coil of electrically conductive bars such as copper wires, are provided in each of slots formed in the cores in the axial direction of each slot. In this configuration, the rotor is rotated in a state where a DC power is supplied from an excitation power source to excite the coils on the rotor side, i.e., the field coils. This induces a voltage in the stator and thereby an electric power is generated.
In a high-speed generator such as a turbine generator, the core of the rotor is generally made from a single steel block so as to ensure mechanical strength against centrifugal force caused at the time of rotation of the rotor.
FIG. 24 is a cross-sectional view of a conventional rotating electric machine. In FIG. 24, reference numeral “1” denotes a rotor core of a rotating electric machine. The rotor core 1 has substantially a circular cross-section and is disposed within a stator core 16 around which an armature coil 15 is wound in a co-axial manner with the same. A predetermined space is interposed between the rotor core 1 and stator core 16. At least one pair of magnetic pole portions 2 and 2 between which a field flux 1 passes are formed at positions on the outer circumference of the rotor core 1 across the center point of the rotor core 1. The area other than the magnetic pole portions 2 and 2 serves as a non-polar portion 3.
A plurality of rotor slots 4 for housing not-shown field coils are formed at predetermined intervals in the non-polar portions 3. Reference numeral “5” denotes a rotor tooth portion formed between the slots 4.
The number of rotor slots 4 for each pole is an integer, so that an interpolar portion 6 is formed in the non-polar portion 3 at substantially the center of the intermediate portion between the pair of magnetic pole portions 2 and 2.
Field coils 7 are housed in the rotor slots 4, and rotor wedges 17 for coils retention are inserted on the outer diameter side of the field coils 7 so as to retain the field coils 7 against centrifugal force caused at the time of rotation of the rotor.
As shown in FIG. 25, the rotor coils 7 are electrically serially connected to one another by connecting pieces 8 at field coil end portions to constitute field coils.
The field coil end portions each includes an end ring 9, an end ring support 10, and an insulating cylinder 11 to thereby retain the field coils 7 against centrifugal force caused at the time of rotation of the rotor.
The centrifugal force applied to the rotor coils 7 housed in the rotor slots 4 shown in FIG. 24 is transmitted to the rotor tooth portions 5 via the rotor wedges 17, and the rotor coils 7 are retained therein. Thus, the widths of the rotor tooth portions 5 are designed such that the rotor tooth portions 5 have sufficient mechanical strength against the centrifugal force.
The field flux generated when the field coils are excited mainly passes through the magnetic pole portions 2 of the rotor core 1 and is supplied to a not shown stator. At this time, the magnetic flux density becomes maximum at a narrowest portions 12 of the magnetic pole portions 2 in general.
When the magnetic flux density is increased, magnetic saturation phenomenon occurs at those portions to lead to a reduction in the field flux. Thus, the narrowest portions 12 of the magnetic pole portions 2 are designed so as to have a width dimension G which prevents occurrence of large magnetic saturation.
There may be a case where cooling gas slots for introduction of cooling gas are provided on the inner diameter side of the rotor slots 4. In this case, the existence of the cooling gas slots may increase the density of the field flux Φ to give any influence on the width dimension G of the narrowest portions 12 of the magnetic pole portions 2.
Thus, the dimensions of the rotor slots 4 are restricted by the width dimension of the rotor tooth portions 5 and width dimension G of the narrowest portions 12 of the magnetic pole portions 2.
In particular, in view of the restriction imposed by the width dimension G of the narrowest portions 12 of the magnetic pole portions 2, it is often the case that, as shown in FIG. 24, the depth of a rotor slots 4a that are formed at the nearest portions to magnetic pole portions 2 are made smaller than the depth of the other rotor slots 4.
In addition, a configuration is disclosed in which disposition of the rotor slots 4 of the rotating direction leading side of the rotor is differentiated from the disposition of the rotor slots 4 of the rotating direction lagging side of the rotor (refer to, e.g., Patent Document 1). Further, a configuration is disclosed in which slits are provided to the surface of the magnetic pole portions 2 (refer to, e.g., Patent Document 2).
All the above-mentioned configurations achieve a reduction in field current under load and suppression of an increase in the temperature of the rotor.    Patent Document 1: Japanese Patent Application Laid-open Publication No. 9-84312    Patent Document 2: Japanese Patent Application Laid-open Publication No. 11-206045